The object of the proposed research is to gain basic information about the Z-band of cross-striated muscle. The planned approach is to study preparations of isolated Z-discs which are prepared by solubilizing all other myofibrillar material with dilute acid. We have purified isolated Z-discs, described their anatomical features, and identified four of the constituent proteins. Specific aims are to purify and chemically characterize these components and to use antibody staining procedures to determine their arrangement within the Z-discs lattice. These studies have acquired special significance in light of numerous recent reports of Z-disc abnormalities associated with both cardiac and skeletal muscle diseases.